I am afraid a full repairing lease is just what it says on the tin. It is a requirement that a lessee first puts the property into full repair and then keeps it in full repair. It is of no
consequence that the property was less than perfect when the lessee took over. Most pubcos make this perfectly clear in their codes of practice and also emphasise that all ingoing lessees should take appropriate advice before they take over the premises. Mrs X's successors will be bound by the same requirements and will wish to ensure that when they leave, they don't pick up liabilities inherited from Mrs X.
That said, a landlord's requirements must be reasonable. Many schedules of dilapidations are downloaded from word processors and include sections as a matter of course. There is usually room for negotiation. Some things will be deleted because their need is a matter of opinion. Others may be included in the new person's proposals for alterations, renovations or refurbishment. It would be a waste of time and money to have them done twice. Some things may not have to be done at all if it can be proved there is no
"diminution to the landlord's reversion" - a legal term that says that the landlord is no worse off if the work is not done.
The best advice I can give Mrs X is to pay another surveyor to negotiate a deal on her behalf and to keep her purchaser in the loop as to what needs to be done, which will have to be negotiated between them - perhaps by way of adjustment to the price paid for the lease.
Ingoing lessees can sometimes eliminate the need to repair certain things - for example the cellar - by agreeing a schedule of conditions before they sign the lease.